This invention relates to the rendering of porous structures impermeable to passage of liquid such as water by treating such porous structures with an aqueous gellable composition containing an amide polymer.
Soil stabilization and grouting have previously been accomplished by forming an aqueous gel in the unstable soil as shown, for example, in U.S. Pat. Nos. 2,856,380 and 2,940,729 wherein a solution containing an ethylenically unsaturated monomer together with a crosslinking monomer such as methylene bis-acrylamide) is pumped into the ground and there polymerized in situ to form a crosslinked gel. Unfortunately, this prior art procedure not only exposes the operator to toxic monomers such as acrylamide but has been found on occasion to allow such toxic monomers to escape polymerization and thereby permeate into the soil water in toxic form. As a result, otherwise potable water sources are endangered.
Preformed, lightly crosslinked polymers and copolymers of acrylamide have been suggested as sorbents or gelling agents for aqueous fluids, for example, in U.S. Pat. Nos. 3,520,925 and 3,810,468. However, the preparation of such polymers or copolymers is very expensive. Moreover, it has been found that it is virtually impossible to reduce the residual toxic monomer content of such crosslinked polymers to an acceptable level for use in products which may come in contact with humans. More importantly, insofar as the use of such pre-crosslinked polymers in soil treating applications are concerned, such polymers are not readily adapted to be pumped into porous soil, cracks in sewers or similar porous structures.
In view of the deficiencies of prior art methods for treating porous structures with polymeric materials to render them impermeable to passage of liquids such as water, it would be highly desirable to provide an improved method for so treating porous structures whereby the polymer to be employed is readily pumped into or otherwise incorporated in the porous structure to be rendered impermeable without polluting the porous structure and its surrounding environment with toxic substances.